1) Field of the Invention
The present invention relates to a method and device for selecting a line in a trunk group within an exchange such as an ATM (Asynchronous Transfer Mode) exchange which handles cells with fixed data lengths.
2) Description of the Related Art
Recently, ATM exchange technology has been agreed as the next generation exchange system by the CCITT (International Telegraph and Telephone Consultative Committee). The ATM exchange technology has been aggressively studied in many institutions to realize as the broadband ISDNs (Integrated Services Digital Networks).
The ATM exchange is characterized in that user information is interchanged in a form of a packet with a fixed length called a cell including contents of unified information (such as data, audio, image) so that information can be transmitted at high speed.
In ATM exchanges, various burst connections are accommodated in the same exchange. The important point is that a resource allocating method uses effectively line resources to take full advantage of traffic characteristics.
Chiefly, both a load distributing system and a squeezing system have been known as a line selecting algorithm in an ATM exchange.
The load distributing system allocates a requested connection to a line with the largest vacant band to provide the same service quality (regarding cell delay, cell discarding rate, or the like) to all connections.
The squeezing system allocates a requested connection to the least vacant band. This system suppresses the fractional releasing effect that a request for larger band cannot be connected because a vacant band is accumulated little by little as connection between plural lines is equally allocated.
However, the conventional method does not perform a line selection, taking account of burst information of a connection to be connected. Hence there is a disadvantage in that the multiple effect is reduced so that the line use efficiency cannot be improved.
The problem above causes that when connections each having a burst characteristic different from another one are allocated to the same line, it is difficult to establish the multiple effect by which peaks and valleys of a burst traffic are mutually canceled because the span between the peaks does not agree with the span between of the valleys.